Sara Lee Corp.'s Sacramento, Calif., facility is a 300,000-sq.-ft. industrial bakery built in 1929. With 450 full-time employees, it produces more than 6 million hot dog and hamburger buns and almost 2 million loaves of bread each week.
Compressed air supports the stacking, blowing and cleaning operations of Sara Lee Bakery's bread-making machines. A compressor replacement helped improve efficiency, but a system-level assessment made the greatest difference, saving $50,000 a year.
Compressed air is important to production because it directly supports the stacking, blowing and cleaning operations required by the bread-making machines. The bakery's compressed air system was served by one 100-hp and two 150-hp rotary screw compressors.
Eventually, the compressed air system's pressure flow controller (P/FC) failed. Air demand patterns began fluctuating severely, and all three compressors had to operate simultaneously so the plant could meet its production targets. The situation was made worse by the fact the compressor controls were out of adjustment. This caused them to react to different control pressures, and more than one compressor would activate when only one unit was actually needed.
Furthermore, compressed air leaks accounted for 15-20 percent of the system's demand, and some uncontrolled open blowing applications were found. Those two conditions exacerbated the pressure fluctuations and wasted even more compressed air.
Plant personnel commissioned Draw Professional Services (DPS) of Cave Creek, Ariz., to evaluate the system. DPS is a company within the Atlas Copco Group, as well as being a U.S. Dept. of Energy (DOE) Allied Partner. Frank Moskowitz, a mechanical engineer with more than 30 years of experience in industrial plant engineering, was sent out. He has worked with DPS for 16 years and has audited hundreds of compressed air systems throughout North America in a variety of manufacturing plants. Moskowitz is a qualified instructor for both the Fundamentals and Advanced Compressed Air Challenge (www.compressedairchallenge.org) training, which are DOE standardized courses, and is a DOE Senior AirMaster+ instructor, one of only three compressed air experts in the country to achieve that status.
His evaluation provided a system-level strategy for improving the compressed air system that involved repairing the P/FC, fixing the compressor controls, repairing leaks and replacing one of the 150-hp compressors with a 100-hp unit fitted with a variable-speed drive (VSD).
Sara Lee invested $38,000 to purchase and install an Atlas Copco GA 75 VSD compressor in late 2004. Like all of Atlas Copco's VSD compressors, the GA 75 optimizes energy consumption by matching compressed air delivery with process demand. This reduces energy costs by an average of 35 percent and overall compressor lifecycle costs by an average of 22 percent.
Now, demand-side leaks are being repaired constantly. The repaired flow controller holds plant pressure at 82 psig. Supply-side pressure is now held at 92 psig, which is 10 psig lower than previously. This equates to an additional 5 percent energy reduction.
After the project, the compressed air system's performance improved considerably, according to Greg Gawlik, assistant chief engineer at the Sara Lee plant. In addition to having a consistent air supply and stable pressure, the plant can now meet its air demand with fewer compressors.
The 100-hp fixed-speed compressor is now the base unit, and the 100-hp VSD unit is the trim compressor. Plant staff were able to dispose of one of the two 150-hp compressors; the remaining one serves as a backup.
The results: The compressed air system project at the Sara Lee Bakery is yielding impressive energy savings while making production more reliable. Measurements taken since the project's completion indicate energy savings of 471,000 kWh annually, for cost savings of $40,000 per year. These figures are consistent with AirMaster+ estimates.
Also, because two compressors are effectively off-line, maintenance costs have declined, saving another $10,000 per year. An $11,000 rebate from the Sacramento Municipal Utility District reduced total project costs to $27,000. With annual savings of $50,000, the project's simple payback was 6.5 months.
"Compressed air systems are found throughout industry, and they can consume a significant portion of the electricity used by manufacturing plants," says Gawlik. "Inoperative and improperly functioning components can reduce compressed air system performance, leading to higher energy and maintenance costs. Using a system-level approach to repairing or replacing malfunctioning components is the best way to optimize system efficiency, reduce energy consumption and ensure reliable production."
This approach employed at Sara Lee's Sacramento bakery can be replicated in many industrial manufacturing plants requiring compressed air.
For more information about Atlas Copco compressors, see www.atlascopco.com or call 413-536-0600. Other resources include the U.S. Dept. of Energy's Energy Efficiency and Renewable Energy program (www.eere.energy.gov) and other DOE case histories at www.oit.doe.gov/bestpractices.